Maui, IMHO, is the best for honeymooners. And make sure its Lahaina/Kaanapali area. Any other they will be bored out of their socks.
My wife and honeymooned on Maui, Kauai, and Oahu, and our favorite by far was Maui. It has all beauty of the other islands, but with more nightlife. Especially the Kaanapali area. Make sure to put multiple resorts in the search. I'd include The Whaler, and Maui Marriott. I'm partial to resorts that are right on the beachwalk way, but of course the Westin is one to consider as well.
If you trade your 2BDRM for a 1BDRM you will really increase your chances of getting a Marriott unit. If they are getting married Sept through Dec, you have a good chance of getting a week. Make plans as soon as you can to increase your chances.
Regards.
Joe